Observing ecosystems with lightweight, rapid-scanning terrestrial lidar scanners

Author Ian Paynter describes how a new wave of terrestrial lidar scanners, optimized for rapid scanning and portability, enable and improve observations of structure across a range of important ecosystems.

Here at the School for the Environment, University of Massachusetts Boston, we study the environment by scanning it with lasers. Our laser scanning instruments utilize light detection and ranging (lidar) technology, sending out pulses of (invisible) light energy, to build up a 3-D image of the surroundings. The School’s research engineer, Francesco Peri, designed and built a small, resilient, and eye-safe terrestrial lidar for our lab, the Compact Biomass Lidar (CBL). This instrument was designed to meet the challenges of diverse ecosystems including temperate and tropical forests, mangroves and saltmarshes. Our paper in Remote Sensing in Ecology and Conservation (RSEC) is about using the CBL to learn about a diverse range of ecosystems through observations of their complicated structure.

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Using a lightweight tower system to deploy Compact Biomass Lidar2 (CBL2) at saltmarsh creeks, Plum Island (MA)

The first moment you see a laser scan of an ecosystem, the potential of the technology is obvious: what you see is a three-dimensional image, acquired in minutes or even seconds, showing objects around you not just recognizably, but in great detail. As you move around and through the point cloud from a laser scan on a computer screen, you can observe objects of interest from a scale and from angles that are not possible on location. It is incredible how much of an ecosystem’s function and condition is represented in the structures that can be seen in the laser scan, e.g. in the types and sizes of trees in a forest or mangrove, or in the shapes of creeks, cliffs and caves. Also what is seen is a moment in time, captured and preserved, allowing us to learn from repeated scans about detailed growth and change.

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Figure 7, from the paper, showing the point cloud (center) colored according to contributions by external (red, green and blue) and internal (yellow) CBL1 scans. Unique structural features observed by the internal scans are shown in isolation (left, yellow).

However, as scientists, our work has to go much deeper than just the potential of a technology. We must also explore the limitations and vulnerabilities, to make sure our findings are robust and complete. Our paper explored both the potential and the limitations of laser scanners for providing information about a diverse range of ecosystems. We investigated, discussed, and suggested solutions for issues of occlusion (where one object blocks the view of another), resolution (the level of detail we can see), and temporal dynamism (when an ecosystem is changing rapidly, even from one minute to the next, such as in tidal ecosystems).

All of our sampling in the field is backed up by tests and calibrations back in our lab, where we can make objects of different sizes, shapes and reflective properties to understand how the laser scanner will see similar objects in ecosystems. Admittedly, these tests of the laser scanner often require moving out into the hallways of UMass Boston, which may inconvenience some passersby, but provides an impromptu learning experience for many others. After all, who doesn’t want to know what they look like in a 3-D laser scan?

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